This application claims the benefit of Korean Application Nos. 01-20495, filed Apr. 17, 2001 and 02-15903, filed Mar. 23, 2002, in the Korean Industrial Property Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a light-emitting device with a structure capable of maximizing light-emitting efficiency, and a display apparatus using the light-emitting device.
2. Description of the Related Art
Silicon semiconductor substrates can be used to highly integrate logic devices, operator devices, and drive devices therein with high reliability. Because silicon is cheap, highly integrated circuits can be formed on a silicon substrate at lower cost, compared to using a compound semiconductor. For this reason, silicon has been used as a base material for most integrated circuits.
Based on the advantage of silicon, steady efforts have been made to manufacture a silicon-based light-emitting device so as to implement a low-cost optoelectronic device that can be manufactured by the general process used to form integrated circuits. It has been experimentally confirmed that porous silicon and nano-crystal silicon have the ability to emit light. Accordingly, research on this idea continues to be conducted.
FIG. 1 illustrates a cross-section of a porous silicon region formed in the surface of a bulk monocrystalline silicon and the energy bandgap between the valence band and conduction band in the porous silicon region.
Porous silicon can be attained by anodic electrochemical dissolution on the surface of bulk monocrystalline silicon (Si) in an electrolyte solution containing, for example, a hydrofluoric (HF) acid solution.
While a bulk silicon is subjected to anodic electrochemical dissolution in a HF solution, a porous silicon region 1 having a number of pores 1a is formed in the surface of the bulk silicon, as illustrated in FIG. 1. In the region where the pores 1a are formed, more Sixe2x80x94H bonds exist than in a projection region 1b, which is not dissolved by hydrofluoric acid. The energy bandgap between the valence band (Ev) and the conduction band (Ec) appears to be inversed with respect to the shape of the porous silicon region 1.
A recession region in the energy bandgap curve, which is surrounded by projection regions and corresponds to the projection region 1b surrounded by the pore region 1a in the porous silicon region 1, provides a quantum confinement effect so that the energy bandgap in this region is increased over that of the bulk silicon. Also, in this region, holes and electrons are trapped, emitting light.
For example, in the porous silicon region 1, the projection region 1b surrounded by the pore region 1a is formed as a quantum wire of monocrystalline silicon to provide the quantum confinement effect, electrons and holes are trapped by the quantum wire and coupled to emit light. The wavelengths of emitted light can range from a near infrared wavelength to a blue wavelength according to the dimension (width and length) of the quantum wire. Here, the period of the pores region 1a is, for example, about 5 nm, and the porous silicon region 1 has a maximum thickness of, for example, 3 nm, as illsutrated in FIG. 1.
Therefore, after manufacturing a porous silicon-based light-emitting device, as a predetermined voltage is applied to the light-emitting device where the porous silicon region 1 is formed, a desired wavelength of light can be emitted depending on the porosity of the porous silicon region 1.
However, such a porous silicon-based light-emitting device as described above is not highly reliable yet as a light-emitting device and has an external quantum efficiency (EQE) as low as 0.1%.
FIG. 2 is a sectional view of an example of a nano-crystal silicon-based light-emitting device. Referring to FIG. 2, the nano-crystal silicon-based light-emitting device has a layered structure including a p-type monocrystalline silicon substrate 2, an amorphous silicon layer 3 formed on the silicon substrate 2, an insulating layer 5 formed on the amorphous silicon layer 3, and lower and upper electrodes 6 and 7 formed on the bottom of the silicon substrate 2 and the top of the insulating layer 5, respectively. A nano-crystal silicon 4 is formed as a quantum dot in the amorphous silicon layer 3.
The nano-crystal silicon 4 is formed in a quantum dot form as the amorphous silicon layer 3 is rapidly heated to 700xc2x0 C. in an oxygen atmosphere for recrystallization. Here, the amorphous silicon layer 3 has a thickness of 3 nm, and the nano-crystal silicon 4 has a size of about 2-3 nm.
In the light-emitting device using the nano-crystal silicon 4 described above, as a reverse bias voltage is applied across the upper and lower electrodes 7 and 6, an intensive electric field is generated at the ends of the amorphous silicon layer 3 between the silicon substrate 2 and the nano-crystal silicon 4 so that electrons and holes in the state of high-energy level are generated. The electrons and holes are tunneled into the nano-crystal silicon 4 and couple to each other therein to emit light. In the nano-crystal silicon-based light-emitting device, the wavelength of light generated therefrom becomes shorter as the size of the nano-crystal silicon quantum dot decreases.
In the light-emitting device using the nano-crystal silicon 4 described above, it is difficult to control the size and uniformity of the nano-crystal silicon quantum dot, and efficiency is very low.
Accordingly, it is an object of the present invention to provide a light-emitting device having a light-emitting efficiency higher than porous silicon-based and nano-crystal silicon-based light-emitting devices and having a double-sided light-emitting structure to maximize light-emitting efficiency, and a display apparatus using the light-emitting device.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and other objects of the present invention are achieved by providing a light-emitting device comprising: a p-type or n-type substrate; at least one doped region formed on at least one surface of the substrate while being doped with a predetermined dopant to be an opposite type from that of the substrate to emit light by quantum confinement in a p-n junction between the doped region and the substrate; and an electrode formed such that the light emitted from the p-n junction of the doped region is externally emitted through both surfaces of the substrate.
The doped region may be formed on one surface of the substrate, and the electrode comprises first and second electrodes formed on a first surface and a second surface of the substrate, respectively, such that the light emitted from the p-n junction of the doped region can be emitted through both first and second surfaces of the substrate. In this case, at least one of the first and second electrodes can be formed as a transparent electrode.
Further, the doped region may comprise first and second doped regions formed on the first surface and the second surface of the substrate, respectively, and the electrode comprises first and second electrodes formed on the first surface and the second surface of the substrate, respectively, to emit light from the p-n junction of the first doped region and third and fourth electrodes formed on the second surface and the first surface of the substrate, respectively, to emit light from the p-n junction of the second doped region, the first and fourth electrodes formed on the first surface of the substrate being separated from each other, and the second and third electrodes formed on the second surface of the substrate being separated from each other.
Further, the substrate may comprise first and second substrates, the doped region may comprise first and second doped regions formed on an outer surface of the respective first and second substrates, and the electrode may comprise first and second electrodes formed on the outer surface of the respective first and second substrates and a common electrode formed between the first and second substrates.
Further, the light-emitting device may comprise a control layer that is formed on the same surface of the substrate as the doped region, acts as a mask in forming the doped region, and limits the depth of the doped region to be ultra-shallow. Further, the substrate may be formed of a predetermined semiconductor material including silicon, and the control layer may be a silicon oxide layer of an appropriate thickness such that the doped region can be formed to the ultra-shallow depth.
The foregoing and other objects of the present invention may also achieved by providing a display apparatus having a plurality of light-emitting devices and enabling bi-directional display, each of the plurality of light-emitting devices comprising: a p-type or n-type substrate; at least one doped region formed on at least one surface of the substrate while being doped with a predetermined dopant to be an opposite type from that of the substrate to emit light by quantum confinement in a p-n junction between the doped region and the substrate; and an electrode formed such that the light emitted from the p-n junction of the doped region is externally emitted through both surfaces of the substrate.